Baylor College of Medicine

West Nile Virus Q&A

BCM Communications

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What is the West Nile Virus?

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West Nile Virus is a virus transmitted by mosquitos that can cause disease mostly in birds, humans, and horses. The virus was first identified in Uganda in the 1930s, then emerged in the Western Hemisphere in New York City in 1999. Since its introduction into the United States, it has spread and established itself across North America. Transmission of the virus from mosquitos typically occurs from the beginning of summer and into the fall.

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How do you get it?

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Most often, people contract this disease through bites from mosquitoes that are infected with the West Nile Virus. Mosquitos become infected from feeding on infected birds. In humans, it can rarely be contracted through blood transfusions, organ transplants, breastfeeding, or from mother to fetus during pregnancy. Donated blood is screened for West Nile virus as a means of prevention of transmission through blood transfusions.

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Is it dangerous?

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It can be, particularly for those individuals who develop severe disease. We have found that 10 percent of those who develop encephalitis (see symptoms below) can die from the infection, and around half of those who survive can experience long-term symptoms, including depression, fatigue, weakness, blurred vision, tremors, headaches, and paralysis.

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What are the symptoms?

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For 80 percent of people infected with West Nile virus, no symptoms are noticed. Around 20 percent of those infected will develop a mild febrile illness, with symptoms that can include fatigue, headaches, fever, swollen lymph nodes, and rash. Rashes are more common in younger patients. Less than one percent of the total people infected with West Nile virus may go on to develop more severe disease known as neuroinvasive disease, which means the virus has invaded the central nervous system and is causing encephalitis, meningitis, and/or paralysis. Those with neuroinvasive disease may experience high fevers, muscle weakness, stiff neck, change in mental status including increased sleepiness and delirium, severe headaches, paralysis, nausea, vomiting, and seizures. Symptoms begin around 3-14 days after the disease has been transmitted from the mosquito.

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What are the treatment options?

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Since this illness is not caused by bacteria, there are no antibiotics available to treat the West Nile virus infection. However, standard hospital supportive care may help decrease the number of complications possible in severe cases.

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Where is it common?

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The virus can be found throughout the continental United States and into Canada.

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Is there anything else we should know?

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If you come across a dead bird, do not dispose of it using your bare hands. Instead, contact your local health department to learn about how to dispose of the carcass appropriately. Also, most mild cases of West Nile virus improve on their own, however, if severe symptoms persist, seek medical attention immediately.

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By: Dr. Kristy Murray, assistant professor of pediatrics at BCM, and Angelene Superable, research assistant in pediatrics at BCM. Both are part of the Baylor College of Medicine National School of Tropical Medicine

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